If you search Google for a hotel, will Google find motels as well? No it won't, but it will find inns, lodging, and accommodations. Yes, Google has an extensive and context sensitive ability to equate your search terms with (what it judges to be) synonymous searches. This is useful for us when we search, but it is also important to know when we are optimizing a website for the search engines.
If you are search engine optimizing your website to rank well on certain search terms it is useful to know what synonyms Google will recognize. For instance, if "sustainable" is an important search term for you, then it would be useful to know if Google will treat "green" as a synonym for "sustainable". The answer is no, Google does not treat sustainable and green as synonyms so for the website I am working on right now, we'll have to optimize for both search terms.
Is there a way to figure out which synonyms Google recognizes? Yes, it's easy. Send me an email and I will reply with an explanation of how to do your own synonym research. Email me at Olin@NorthStarInternet.com